Image sensor including pixel circuits for event detection connected to a column signal line

Abstract

An image sensor includes a plurality of pixel circuits for event detection, wherein each pixel circuit includes at least one output transistor and at least one selection transistor electrically connected in series between at least one pixel output and a first supply potential. A column signal line electrically connects the pixel outputs of the plurality of pixel circuits. A comparator/latch circuit is configured to receive a signal derived from a pixel event signal transmitted on the column signal line at a first comparator input, and to output a latched active column event signal, when the signal at the first comparator input exceeds or falls below a threshold voltage applied to a second comparator input of the comparator/latch circuit.

1 . An image sensor, comprising:
 a plurality of pixel circuits for event detection, wherein each pixel circuit comprises at least one output transistor and at least one selection transistor electrically connected in series between at least one pixel output and a first supply potential;   a column signal line electrically connecting the pixel outputs of the plurality of pixel circuits; and   a comparator/latch circuit configured to receive a signal derived from a pixel event signal transmitted on the column signal line at a first comparator input, and to output a latched active column event signal, when the signal at the first comparator input exceeds or falls below a threshold voltage applied to a second comparator input of the comparator/latch circuit.   
     
     
         2 . The image sensor according to  claim 1 , further comprising:
 a first switch element configured to electrically couple the column signal line and the second comparator input via a low impedance path in response to an initialization signal.   
     
     
         3 . The image sensor according to  claim 1 , further comprising:
 a reference voltage source configured to generate a constant reference voltage, wherein the threshold voltage is derivable from the reference voltage.   
     
     
         4 . The image sensor according to  claim 1 , further comprising:
 a current source circuit comprising a current source transistor electrically connected between the column signal line and a second supply potential.   
     
     
         5 . The image sensor according to  claim 4 ,
 wherein the current source circuit comprises a bias voltage circuit configured to pass a supply voltage dependent bias voltage to the gate of the current source transistor.   
     
     
         6 . The image sensor according to  claim 1 , further comprising:
 a bias disabling circuit configured to disable biasing of the column signal line in response to a bias disable signal.   
     
     
         7 . The image sensor according to  claim 1 ,
 wherein each pixel circuit comprises a pixel photocurrent circuit configured to output a pixel voltage signal proportional to incoming light intensity, a voltage buffer configured to generate a shifted pixel signal by shifting a voltage level of the pixel voltage signal by an amount determined by a voltage level of the pixel voltage signal at a reset time, and a pixel logic circuit configured to output the pixel event signal based on a result of comparisons of the shifted pixel signal with a first reference voltage and a second reference voltage.   
     
     
         8 . The image sensor according to  claim 1 , further comprising:
 a voltage bias element configured to cause a voltage bias at the first comparator input or the second comparator input.   
     
     
         9 . The image sensor according to  claim 1 , further comprising:
 a first switch element configured to electrically couple the column signal line and the second comparator input via a low impedance path in response to an initialization signal;   a capacitive element configured to couple the pixel event signal to the first comparator input, and   a second switch element configured to electrically couple the first comparator input and the second comparator input via a low impedance path in response to the initialization signal;   
     
     
         10 . The image sensor according to  claim 1 ,
 wherein the comparator/latch circuit comprises a comparator circuit and a latch circuit, wherein the latch circuit is configured to latch a comparator output signal of the comparator circuit in response to a trailing and/or falling edge of a latch signal.   
     
     
         11 . The image sensor according to  claim 1 ,
 wherein the comparator/latch circuit comprises a latch comparator, wherein the latch comparator includes a tail transistor and a differential pair, wherein the differential pair comprises a first input transistor and a second input transistor, wherein the first comparator input is connected to a gate of the first input transistor, wherein the second comparator input is connected to a gate of the second input transistor, and wherein load paths of the differential pair are connected in parallel to each other between a hold circuit and a load path of the tail transistor.   
     
     
         12 . The image sensor according to  claim 11 , further comprising:
 a capacitive element and a preamplifier circuit, wherein the capacitive element is configured to pass the pixel event signal to an input of the preamplifier circuit, and wherein the preamplifier circuit is configured to amplify the pixel event signal passed to the input of the preamplifier circuit and to supply an amplified pixel event signal to the first comparator input or the second comparator input.   
     
     
         13 . The image sensor according to  claim 12 ,
 wherein the preamplifier circuit is further configured to electrically connect the first comparator input, the second comparator input and the input of the preamplifier circuit in response to an active reset signal.   
     
     
         14 . The image sensor according to  claim 1 , further comprising:
 a transimpedance amplifier circuit comprising an operational amplifier, wherein the operational amplifier is configured to receive the pixel event signal at one of a non-inverting input and an inverting input, and a reference voltage at another one of the non-inverting input and the inverting input, and wherein the transimpedance amplifier circuit is configured to pass a signal derived from an output signal of the operational amplifier to the first comparator input of the comparator/latch circuit.   
     
     
         15 . The image sensor according to  claim 1 ,
 wherein each pixel circuit comprises a complementary output transistor and a complementary selection transistor electrically connected in series between a complementary pixel output and the first supply potential, and wherein the image sensor further comprises:   a complementary column signal line electrically connecting the complementary pixel outputs of the plurality of pixel circuits,   and wherein the comparator/latch circuit is further configured to receive a signal derived from a complementary pixel event signal transmitted on the complementary column signal line at the second comparator input.